The Unfinished Tales is best regarded as volume 0 of The History of Middle-earth (or volume 13, depending on your point of view). The Children of Húrin is actually the expansion of one chapter from The Silmarillion, most of its material having already appeared in Unfinished Tales or History 10&11. So they're both closely related.

Perilous Realm is not closely related. It contains 'fairy stories' not set in M-e. But they're still related to Tolkien's philosophic concept of mythology and fairy stories that is also behind M-e.

Posted on: 2008/6/20 20:33

_________________Then in the name of the king, go and find some old man of less lore and more wisdom who keeps some in his house! - Gandalf in Minas Tirith [LR 5 VIII:70]